The present invention relates to vehicle wheel alignment, and more particularly to systems for rapidly and reliably testing steering lash and suspension play.
Tests are known for checking steering wheel lash and suspension play. These tests are predominantly manual, not particularly accurate and relatively time consuming. For example, a standard suspension play test requires hoisting the vehicle, applying the brake to eliminate wheel bearing movement, manually grasping the front and rear of one of the front tires and attempting to move the wheel/tire assembly right and left without moving the steering gear. If the measured movement at the front or rear of the tire is greater than a predetermined amount (such as 1/4 inch), then the test is failed. Note that if the tire is grasped at the front and the rear as directed, it is at least inconvenient for a single user to also measure the movement of the wheel/tire assembly.
Standard tests for steering wheel lash are similarly deficient. For example, one such procedure reads:
"With road wheels in straight ahead position, turn steering wheel until motion can be detected at the front wheels. Align a reference mark on steering wheel with a mark on a ruler and slowly turn steering wheel in the opposite direction until motion can again be detected at the front road wheel. Measure lash at steering wheel. Special lash-checking instruments are also available, measuring free play in inches or degrees. Such instruments should always be mounted and used according to the manufacturer's instructions.
"Reject Vehicle: If steering wheel movement exceeds:
Power--2 inches (51 mm) PA1 Manual--3 inches (76 mm)"
Note that this procedure requires detecting motion at the front road wheels, which is difficult to do accurately without instruments, while at the same time one is turning the steering wheel. The user must also measure, with a ruler or with a lash-checking instrument, the movement of the steering wheel during the procedure. As can be readily be appreciated, this procedure is slow, inaccurate and may require more than one person to perform properly.
A method for monitoring ball joint wear is shown in U.S. Pat. No. 4,574,490, but that particular method is fairly limited in the particular defect that it detects and requires both camber and toe to be measured at least twice. This method also requires external forces on the tires, which is not always desirable. The '490 patent also typically requires a fairly highly trained technician to operate.
Also known, although apparently not used in the context of checking steering lash and suspension play, are various systems designed to determine vehicle wheel alignment angles. For example, U.S. Pat. No. Re33,144 to Hunter and January and U.S. Pat. No. 4,319,838 to Grossman and January each describe a wheel alignment system which uses electro-optical transducers to determine the toe alignment angles of a vehicle. FIG. 2 of each of these patents shows six angle transducers carried by support assemblies which are mounted to the vehicle wheels. FIG. 4 of Re33,144 and FIG. 9 of U.S. Pat. No. 4,319,838 show the geometry of this arrangement and illustrate the six angles which are directly measured. These patents further describe (see Re33,144 col. 7 lines 26-39, and U.S. Pat. No. 4,319,838 col. 8 line 63 to col. 9 line 12) how the toe alignment angles are computed from the angles directly measured by the angle transducers. The disclosures of these patents is hereby incorporated herein by reference.
SAE Publication 850219, titled "Steering Geometry and Caster Measurement", by January, derives and discusses the procedures and methods by which toe and camber alignment transducers are used to determine the caster and steering axis inclination (SAI) of a vehicle. The procedures described therein are the industry standard. The disclosure of this publication is hereby incorporated herein by reference.
Equipment of this general type and using the apparatus and methods enumerated above has been used world-wide for many years. Such equipment is capable of determining the camber, caster, and pointing or "toe" alignment angles of the wheels relative to one or more appropriate reference axes, and is sufficient to allow proper adjustment of the alignment so as to reduce tire wear and provide for safe handling. It is believed, however, that such equipment could be improved.
German Patent DE 29 48 573 A1, assigned to Siemens AG, describes the use of cameras to determine the locations and orientations of the wheels of a vehicle. On each side of the vehicle, a single camera is moved to multiple positions to view the vehicle wheels. Alternatively, a single fixed camera is used at each side in conjunction with movable mirrors, or multiple cameras are used. The system examines the images thus viewed of the wheels of the vehicle to determine the locations and orientations of the wheels, from which the wheel alignment parameters are determined.
European Patent Application PCT/US93/08333, filed in the name of Jackson and published under the Patent Cooperation Treaty as WO 94/05969 (hereinafter referred to as WO document 94/05969), describes the use of a camera having one or more defined fields of view to view optical targets of known configurations which are mounted to the vehicle wheels. Through the use of sophisticated image recognition methods, the three dimensional coordinates and orientations of the vehicle wheels and their corresponding axes of rotation are determined. The wheel alignment parameters are determined from these coordinates and orientations. The disclosure of this document is hereby incorporated herein by reference, as are the disclosures of U.S. Pat. Nos. 5,675,515, 5,724,128, 5,489,983, 5,488,472, and 5,488,471.
It is not believed that heretofore such alignment equipment has been considered for use in testing steering lash or suspension play. Moreover, it should be noted that if steering lash or suspension play is excessive it may in fact be very difficult to perform a proper alignment on a vehicle even using these sophisticated alignment techniques shown in the references cited above.